Applicant's U.S. Pat. No. 6,883,446 issued on 26 Apr. 2005 describes an apparatus which permits a user to manually move a stack of fabric layers across a planar bed beneath a stitch head. The apparatus includes a detector for detecting the movement of the stack for the purpose of synchronizing the delivery of stitches to the stack movement. This approach enables the insertion of uniform length stitches while allowing the user to freely move the stack within a wide range of speeds, to start or stop the stack movement at will, and to guide the stack in any direction across the planar bed.
The preferred embodiments described in said U.S. Pat. No. 6,883,446 employ a detector configured to detect stack movement within the throat space of a quilting/sewing machine by measuring the movement of at least one surface of the stack as it moves across the planar bed. As described, a preferred detector responds to energy, e.g., light, reflected from a target area on the stack surface (top and/or bottom) within the machine's throat space. The detector preferably provides output pulses representative of incremental translational movement of the stack along perpendicular X and Y directions. The output pulses are then processed and used to control the stitch head actuation rate.
Applicant's U.S. Pat. No. 6,883,446 primarily contemplates that a user directly grasp, or touch, the stacked fabric layers to push and/or pull the stack across the planar bed. However, the application also recognizes that the user could, alternatively, mount the stack on a quilt frame and then grasp the frame to move the stack across the planar bed to enable the detector to sense stack surface movement.
Applicant's U.S. Application 60/571,109 filed 14 May 2004, which is incorporated herein by reference, describes alternative embodiments for controlling stitch head actuation which involve using a frame for mounting the fabric layer stack. The frame is supported for user guided movement beneath a fixedly located stitch head and a detector is provided to produce signals representing the magnitude of frame translation, and thus the magnitude of stack translation.
Applicant's parent application Ser. No. 11/443,563 describes a further method and apparatus for controlling stitch head actuation as a function of stack movement based on the recognition that thread is pulled, or paid out, from a top or bottom bobbin, or spool, in direct relationship to the movement of the stack. By detecting the longitudinal movement of the thread, control circuitry can respond to control the rate of stitch head actuation. As a consequence, uniform length stitches can be produced as the stack is freely manually guided across the planar bed.
The thread payout detector embodiments described in said application Ser. No. 11/443,563 rely primarily upon sensing the rotation of a mechanical member, e.g., an encoder carried by a thread supply spool (FIG. 8) or a thread driven gear (FIG. 14A). Although such embodiments can function satisfactorily under some circumstances, various mechanical factors can adversely affect their performance; e.g., slippage between the thread and rotating member, potential contact damage to the thread, increased thread drag, etc. One detector embodiment (FIG. 11) described in said application Ser. No. 11/443,563 avoids physical contact with the thread by employing an optical sensor for detecting uniformly spaced features of the thread.